Behavioral research is at the heart of the NIH's mission of gaining fundamental knowledge about the nature and behavior of living systems. Sensory systems with simple circuitry and a direct influence on the behavior of the organism and that also apply broadly to us as complex mammals are difficult to find. The accessory olfactory system in mammals provides us with such a system with its simple circuitry and direct effect on the behavioral, hormonal and metabolic state associated with pheromones. In addition, it provides us with a simple system in which to study the organization and integration of input that directly modulates the overall behavior of higher level mammals. As is the case with any sensory system, understanding the nature of input and its representation within the system is critical to understanding how the system performs its function. In the case of the accessory olfactory system, sensory neurons in the vomeronasal organ (VNO) bind non-volatile pheromones and project and synapse on the primary output neuron (mitral cells) of the accessory olfactory bulb (AOB), in glomeruli. Determining the nature of vomeronasal sensory neuron input onto AOB mitral cells and how they represent this information is critical for understanding how this sensory system integrates and encodes information to achieve its remarkable combination of sensitivity and selectivity to affect the behavior of the organism. The overall goal of this project is to determine the rules that govern the connectivity from the VNO to the accessory olfactory bulb mitral cells. We will accomplish this goal using both electrophysiological and anatomical approaches in both transgenic V2R-GFP mice and wildtype mice. First, we will determine the degree of overlap in populations of mitral cells following stimulation of glomeruli of the same or different vomeronasal receptors types. We will test whether mitral cells receive homogenous vs. heterogenous input by comparing the degree of overlap with hypotheses for each. Second, we will analyze the dendritic tufts of mitral cells which show calcium transients upon stimulation of specific glomeruli using confocal imagery. We will determine if mitral cells send their tufts exclusively to glomeruli of the same VN receptor type or different. More importantly, understanding the logic and organization underlying these circuits allows for the identification of fundamental principles present in the great varieties of circuits found in sensory systems. These principles can then provide a conceptual framework for understanding how the brain is processing and integrating the vast amount of information it receives constantly and what goes wrong in these circuits that affects the health of individuals and their ability to receive and process sensory stimuli.